Allocation and adjustment of communication resources is becoming increasingly important with the ever-escalating profusion of users and devices. In Public Safety systems, such as ASTRO systems, resource efficiency and allocation, especially during a crisis, may be of paramount importance. Many communication systems typically deploy a “star” topology, in which a master system site (also referred to as a core) connects to a number of remote system sites (RF/repeater sites, console sites, combinations thereof), and communications between the different remote system sites traverse the master system site. In such systems, a logical connection (layer-2 or layer-3 connection, such as an IP tunnel) is established between the master system site and each site, and audio traffic between sites traverses these logical connections. This star topology is especially prevalent in Public Safety or other systems with end-to-end Ethernet or IP solutions, which will only increase as customer demand for packet based services from carriers become cheaper and more ubiquitous.
Although each site has a unique logical connection to the master system site, many or all of these logical connections may traverse the same physical link. Even if the system sites themselves are geographically close or even connected physically, and even though most of the sites are likely to be geographically distant from the master system site, traffic between system sites still is routed to the master system site through the physical link. As multiple resources are sharing the link, the physical link between the sites and the master system site has much larger throughput than any site-to-site connections that may be present. The star topology also substantially limits flexibility in arranging sites in the communication system.
Each system site may have a conventional site and a trunked site for servicing calls from subscribers serviced by the site. These individual system sites are connected through a router to the master system site to enable the master system site to communicate with the individual system sites. A zone controller is typically located at the master system site and a conventional site controller and a dispatch console are typically located at one of the system sites to coordinate call resources within the communication system. When a radio keys up (requests the floor for audio transmission), the individual site servicing the radio requests resources from the zone controller. During normal multicast operation, when a conventional resource is requested on a particular channel by the radio, the zone controller grants or denies the request, assigning a multicast address when the request is granted. Similarly, when a trunked resource is requested by the radio, the zone controller grants or denies a channel from a predetermined set of channels and assigns a multicast address to that channel when the request is granted. The dispatch console (and dispatcher) coordinates activities and communication along the channels.
During normal operation (the normal system state), traffic is not routed from one system site through another to reach the master system site, as a direct path exists to the master system site. Furthermore, traffic intended to go from one system site to another traverses the master system site, going from the source system site through the master system site to the destination system site. However, the star topology is problematic in the event that the physical link to the master system site is lost or the master system site fails (failure system state). In either case, each of the logical connections traversing the link is also lost and each of the sites becomes isolated. Since access to the controller or dispatch console follows the logical connections, loss of these connections isolates sites from reaching the controller and dispatch console, resulting in subscribers at the isolated sites being unable to contact dispatchers and perhaps other subscribers. Since the long-distance physical connection may not be highly reliable, there is significant risk of isolating multiple sites due to this single failure.
Even if site-to-site connections exist, as the bandwidth between the sites may only be provisioned to support a limited amount of the overall system traffic, direct connectivity between the individual system sites may not be permitted or the amount of traffic may be severely limited. It thus would be desirable to provide a more flexible arrangement that permits at least a limited amount of multicast communication between sites when connectivity to the master system site is lost by multiple system sites.
Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help improve understanding of various embodiments. In addition, the description and drawings do not necessarily require the order illustrated. It will be further appreciated that certain actions and/or steps may be described or depicted in a particular order of occurrence while those skilled in the art will understand that such specificity with respect to sequence is not actually required.
Apparatus and method components have been represented where appropriate by conventional symbols in the drawings, showing only those specific details that are pertinent to understanding the various embodiments so as not to obscure the disclosure with details that will be readily apparent to those of ordinary skill in the art having the benefit of the description herein. Thus, it will be appreciated that for simplicity and clarity of illustration, common and well-understood elements that are useful or necessary in a commercially feasible embodiment may not be depicted in order to facilitate a less obstructed view of these various embodiments.